If your African violet has developed yellow-white splotches and rings on it's leaves
this winter, it is most likely due to watering practices rather than some strange disease.

The rings and spots probably are related to the temperature of the irrigation water.
Its not unusual for African violets to develop these symptoms during winter because
tap water is colder than during other times of the year.

African violets are sensitive to the differences between the air temperature and water
temperature, and they develop spots when the water is colder than the air. You
probably didn't notice the problem before because the difference in temperature between
the two wasn't that great. From now on, use room-temperature water. Avoid
splashing water onto the leaves. Even with the change in water temperature, the
spots won't disappear, but leaves that develop in the future won't be affected.